The subject matter disclosed herein generally relates to a motors and motor control and, more particularly, to a new architecture for a variable frequency variable voltage multilevel drive.
Aircraft systems commonly include a variety of motor controlled systems. For example, motor controlled systems can include actuation systems for control surfaces, aircraft components environmental control systems, and the like. In some systems, such as actuation systems for control surfaces, power quality can impact control systems limit their capability to achieve higher speeds, maintain loads, and design criteria.
Conventional motor drive systems, particularly in an airborne environments, are expected to operate under a variety of input power conditions that commonly exceed specifications. For example, in some instances aircraft power systems can exhibit Total Harmonic Distortions (THD) 30% higher than specified and power factors as low as 0.75. Commonly, these conditions worsen as power loads increase.
Aircraft power generation systems are often configured to regulate the bus voltage and current over a relatively small range of loads. As a result, and especially with very small or very large loads, it is common for aircraft generator systems to not be able to meet the bus regulation as expected. Moreover, in simple passive motor drives, the DC bus formulated from a given AC input varies widely with any variation in the input AC input voltage from an aircraft power generation system. One solution for these issues is to employ motor drives that are oversized/overdesigned and conservatively configured to ensure operations at a variety of input voltage and current ranges. However, oversizing components can be inefficient, and expensive. Similarly, overdesigning or conservatively designing motor drive components usually requires larger and heavier components. Moreover, as power levels increase, passive solutions for motor drives become very bulky and heavy and not well suited to airborne applications, primarily a result of the larger size and weight of magnetics, and the direct current (DC) Link capacitor typically employed in motor drives.
Therefore what is needs is a motor drive capable of providing for increasing speed and torque requirements while operating from power sources that exhibit limited power quality.